Liquids are combined or mixed in many industrial processes. For example, liquids are mixed in the manufacture of products such as chemicals, medications, detergents, paints, and integrated circuits. Liquids are also mixed in treating water for human consumption, or for use in manufacturing. Liquids are mixed for example by pumping one liquid into a container that contains another liquid. It is often difficult to control the amount of a second liquid that is being added to a first liquid.